The present invention relates to a drive control apparatus for controlling driving of a forklift.
Conventionally, forklifts are widely used as industrial vehicles for handling loads (picking up and placing of loads) in plants. Due to its characteristic usage, the driving stability of this type of forklift greatly varies depending on the load state. For example, the center of gravity of the vehicle is shifted and the driving stability varies between a state of carrying no loads and a state of carrying a load. When carrying a load, the driving stability varies depending on the weight of the load, the height of the fork on which the load is mounted, the tilt angle of the fork. Thus, conventionally, techniques for limiting the driving of a forklift to improve the driving stability of the vehicle have been disclosed in Japanese Laid-Open Patent Publication Nos. 2001-31391 and 2001-163597. The technique disclosed in the publication No. 2001-31391 limits the vehicle speed in accordance with the load state of the forklift. In the publication No. 2001-163597, the minimum value of acceleration that causes rear wheels to be raised off the ground surface when the vehicle is moving rearward is computed based on the load state and is set as a permissible acceleration. The actual acceleration of the vehicle is limited not to surpass the permissible acceleration.
Driving of a forklift can be unstable during acceleration or deceleration. Thus, in order to further improve the driving stability of the forklift, limitation is preferably put on acceleration/deceleration of the vehicle in addition to limitation on the vehicle speed disclosed in publication No. 2001-31391.In this respect, the publication No. 2001-163597 limits driving of a forklift by taking into consideration the acceleration of the forklift at the start (when the forklift is reversed).
However, according to Japanese Laid-Open Patent Publication Nos. 2001-31391 and 2001-163597, in which the driving of a forklift is limited, changes in the contents of limitation are not taken into consideration. That is, no control procedure is executed for ensuring the driving stability at such changes. That is, during the driving of a forklift, the load state can be changed when the fork height is lowered or when the tilt angle is changed. Therefore, in a forklift the driving of which is limited, the contents of limitation are changed when the load state is changed during driving. For example, in a state where the vehicle speed of a forklift is limited while the fork height is high, if the fork height is lowered and the limitation on the vehicle speed is cancelled, the forklift is accelerated in accordance with the amount of depression of the accelerator pedal, and the vehicle speed is increased, accordingly. In this case, the forklift can be abruptly accelerated or decelerated in response to a change in the contents of limitation. Such a sudden change in the vehicle speed can result in an unstable driving.